Anisotropy-Induced Soliton Excitation in Magnetized Strong-Rung Spin Ladders
We report low temperature electron spin resonance experimental and theoretical studies of an archetype S=1/2 strong-rung spin ladder material (C5H12N)2CuBr4. Unexpected dynamics is detected deep in the Tomonaga-Luttinger spin liquid regime. Close to the point where the system is half-magnetized (and believed to be equivalent to a gapless easy plane chain in zero field) we observed orientation-dependent spin gap and anomalous g-factor values. Field theoretical analysis demonstrates that the observed low-energy excitation modes in magnetized (C5H12N)2CuBr4 are solitonic excitations caused by Dzyaloshinskii-Moriya interaction presence.